Polishing agent and polishing method

ABSTRACT

In order to polish an insulating film, a cerium oxide polishing agent (ceria slurry) is used. The ceria slurry is composed of cerium oxide powder containing Na, Ca, Fe, and Cr concentration of which is less than 10 ppm. Fragile inorganic and organic insulating films formed at relatively low temperatures can be polished without degrading the characteristics of the semiconductor element due to Na diffusion.

This application is a Divisional application of application Ser. No.08/531,910, filed Sep. 21, 1995, now U.S. Pat. No. 5,772,780, IssuedJun. 30, 1998 the contents of which are incorporated herein by referencein their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a polishing agent and a polishingmethod for polishing the surface of an insulating film or a coatinginsulating film constituting a semiconductor integrated circuit or anoptical glass element.

When a semiconductor integrated circuit is manufactured with a wiringsubstrate of silicon, a variety of insulating films are used and theirsurfaces need to be machined into predetermined shapes. Polishing hasbeen widely used as an effective technique for planarizing or smoothingthe surfaces of the insulating films. Especially in the machining of asemiconductor integrated circuit, the chemical mechanical polishing(hereinafter referred to as the "CMP") has been examined for planarizingthe surfaces. In Proceedings VLSI Multilevel Interconnection Conference,pp. 20-26, 1991, for example, there is disclosed a method for polishingand planarizing an SiO₂ film using a polishing agent (hereinafterreferred to as the "silica slurry") prepared by dispersing fine SiO₂particles (colloidal silica or fumed silica) in an aqueous solution ofpotassium hydroxide (KOH). It is well known that the addition of thechemical reaction effect accelerates the polishing rate (hereinafterreferred to as "removal rate") by keeping the liquid alkaline in aregion where the pH value is higher than 7. However, the neutral regionactually varies within a pH range of 6.5 to 7.5. Therefore, the solutionis actually stable as an alkali in the pH region over 7.5 and as an acidin the pH region below 6.5.

When an insulating substance such as of a glass substrate other than athin film used for manufacturing a lens and a liquid crystal displayelement, especially, a substance composed mainly of SiO₂ is polished,there is a known polishing agent (hereinafter referred to as the "ceriaslurry") using cerium oxide powder. This ceria slurry is explained, forexample, in Kikai no Kenkyu, volume 39, No. 12, pp. 1296-1300, 1987, andErekutoronikusuyo kessyozairyonoseimitukakogijutu, pp. 251-256, SaiensuForamu Co., Tokyo, 1985. The actual polishing is effected by mixingcerium oxide powder in water. In the prior art polishing method usingthe ceria slurry, a mixture of the cerium oxide powder and water ismerely used as the polishing agent. In short, the ceria slurry is notexpected to exhibit a chemical effect using acidity or alkalinity but isused to bring about the so-called "mechanical polishing effect."

The ceria slurry can be applied to optical glass elements or the likebut will degrade the characteristics of a semiconductor integratedcircuit if applied to the process of manufacturing a semiconductorintegrated circuit. If the insulating film on a bipolar transistor, forexample, is polished by the ceria slurry and is subjected to a heattreatment essential for the semiconductor manufacturing process, thecurrent amplification factor h_(fe) of the bipolar transistor markedlylowered. If, moreover, the insulating film on a diode is polished byusing the ceria slurry, there arises a problem that the rectifyingcharacteristics of the diode deteriorate.

SUMMARY OF THE INVENTION

An object of the present invention is to polish the insulating film of asemiconductor element or the like without degrading the characteristicsof the semiconductor element.

The above-specified object is achieved by using a ceria slurrycontaining cerium oxide powder which contains impurities of less than 10ppm of Na, Ca, Fe and Cr in total.

If the ceria slurry of the prior art is used for polishing, thecharacteristics of the semiconductor integrated circuit are degraded dueto the low purity of the cerium oxide powder. The analysis of the ceriaslurry of the prior art has revealed that the contents of impuritiessuch as Na, Ca, Fe and Cr are from about 1 to about 20 ppm, their totalexceeds 50 ppm, and the polishing agent contains many other metals. Inshort, these impurities adversely affect the current characteristics ofthe transistor. The impurity Na diffuses into the aforementioned bipolartransistor to lower the current amplification factor. When a coatingfilm containing as little as 2 ppm of sodium (Na) is in contact with thesurface of a semiconductor element such as a bipolar transistor, and theelement is subjected to a heat treatment at 450° C. for about 30minutes, the diffusion of Na seriously reduces the current amplificationfactor h_(fe) of the bipolar transistor, as disclosed in Denshi Tokyo,IEEE Tokyo Section, pp. 70-73, 1981. The requirement of the impurityconcentration is less than 10 ppm in accordance with the presentinvention. This value is larger than the threshold value of less than 2ppm. If the concentration is less than 10 ppm, when cerium oxide powderis dispersed in water, the impurities in the cerium oxide particlesdissolve little into water, so that any of the impurity concentrationsin the dispersing liquid is less than 1 ppm and there arises no problemof Na diffusion or the like. Moreover, Ca is attached to and mixed withNa, that is, Ca is usually present anywhere Na is present. In order toreduce the Na concentration, it is essential to reduce the Ca content.Moreover, the presence of Fe and Cr degrades the rectifyingcharacteristics or the like of the diode. With the increase in theleakage current, for example, the characteristics of a Schottky barrierdiode will approach ohmic characteristics.

Unlike the aforementioned colloidal silica, the cerium oxide powder isgenerally extracted from an ore containing many impurities and thenpurified and pulverized, so that the characteristics vary according tothe mine of the ore and the method of processing the particles.

The amount of Cr in cerium oxide powder is less than 10 ppm, therefore,the adverse effects can be prevented even if ceria slurry, used as thecerium by keeping the concentrations of Na, Ca, Fe and oxide powder, isused for machining semiconductor integrated circuits. In the course ofrepeating polishing, moreover, impurities may be accumulated in thepolishing apparatus or container and may be a source of contamination.Hence, the concentration of the Na contaminant is desirably suppressedto no more than 2 ppm.

When the impurity concentration is less than 10 ppm, if the ceria slurryis prepared by dispersing the cerium oxide powder into water, theimpurities in cerium oxide powder hardly dissolve into the liquid sothat any impurity concentration in the liquid in which ceria isdispersed (is mixed into solvent to be used) is less than 1 ppm to causeno problem of Na diffusion or the like. Incidentally, if thecontamination should be strictly avoided, it is necessary to a suppressthe concentration of each of the Na, Ca, Fe,Cr and K in the dispersionto no more than 0.1 ppm. When, moreover, the concentration of the ceriumoxide powder in the dispersion is 5% or more, the dependency of thepolishing rate upon the concentration is lowered to stabilize thepolishing operation.

When, moreover, the prior art ceria slurry having a high impuritycontent was used for the polishing, many polishing scratches causingdefective products were formed in the manufacture of wiring substratesfor semiconductor integrated circuits and the like. There were visuallydetectable five to ten polishing scratches in the area of a diameter ofabout 4 inches. These scratches are thought to have been formed by asmall number of large particles contained in the ceria slurry. It hasalso been found that the polishing scratches are liable to be formedespecially in a low density and fragile film such as a CVD (ChemicalVapor Deposition) film formed by a chemical reaction at a lowtemperature less than 500° C. or organic and inorganic coating film.This is because the cerium oxide powder of the prior art has an averageparticle size exceeding 1 μm. It has been found that the polishingscratches are suppressed if the average particle size is less than 1 μm.The average particle diameter is preferably 0.3 μm or less especiallyfor a fragile and soft organic insulating film. Here, cerium oxideparticle size means a larger value obtained from either individualparticle size or aggregated particle size. Average particle sizeexpresses the average value of the measured particle size distribution.Since an organic insulating film generally has a low dielectricconstant, a multilevel wiring technique can be achieved to polish andplanarize the insulating film so that the capacitance between theadjacent wirings can be reduced by several tens of percentage points.The degree of producing polishing scratches has a relation to not onlythe material to be polished but also generally the polishing depth.Thus, there is a tendency that more polishing scratches are formed asthe polishing depth becomes larger. By using the ceria slurry of thepresent invention, however, scratches are small even though thepolishing depth was greater, and serious scratches causing defects arenot observed. Further, using a polymer polishing pad on a polishingplaten rather than a hard polishing platen is effective to suppresspolishing scratches during polishing.

It has also been found for the cerium oxide that there are two kinds ofcerium oxide powder having very different polishing characteristics.Specifically, one kind of cerium oxide powder is the one (ceria A) whosecolor quickly changes while foaming into dense yellow when it is mixedin an aqueous solution of hydrogen peroxide; and the other kind (ceriaB) which hardly changes in color and slightly foams. These two kindshave substantially identical chemical compositions but vastly mutuallydifferent crystallite sizes of the particles. It can be considered fromthe results of an X-ray diffraction analysis that the former is anaggregate of fine particles having a small crystallite whereas theindividual particles of the latter powder are substantially crystals.For example, the half value of the ceria A of the diffraction peak forthe crystal orientations (111), (200) and (220) is no less than 0.5whereas that of the ceria B is not more than 0.3. By half value, we meanthe full width of the half maximum (FWHM). Moreover, the cerium oxide Ahas a crystallite size of not more than 30 nm for the above-specifiedcrystal orientations whereas the cerium oxide B has a larger crystallitesize of not less than 60 nm.

Cerium oxide A is suitable for selectively polishing an organicinsulating film (which means, in this Specification, a film of a siliconcompound containing 1% or more of organic components in the film.Concentration of organic components is expressed as the weightpercentage of carbon and hydrogen in the films to the whole filmweight.), and polishing an organic insulating film and a doped ornondoped insulating film at substantially equal rates. Selective CMP canbe more stably carried out when the relative dielectric constant of theorganic film is not larger than 3.5. Increasing the organic component tono less than 10% is effective for decreasing moisture absorption in theorganic film. However, polishing polyimide film which is a very popularpolymer as a highly reliable material using the cerium oxide A powdergenerates many polishing scratches, and could not provide good polishedsurface. In the Specification, a doped insulating film means aninorganic insulating film containing 0.1% or more of boron, phosphorusand other metallic impurities; a nondoped insulating film means aninorganic silicon compound insulating film containing silicon oxide asits main component but not any organic component, and containing 0.1% orless of boron or phosphorus. These organic insulating films and dopedinsulating films can be formed by coating. Cerium oxide B is suitablefor polishing mainly doped and nondoped insulating films at a high rate.

For these uses, we have examined the method of controlling the exponentof hydrogen ion concentration pH value of the dispersion of the ceriumoxide powder. The cerium oxide powder has been conventionally used in asubstantially neutral liquid in the prior art. Here, the neutralitypractically indicates that the hydrogen ion concentration is within arange of pH value about 6.5 to 7.5. Such a wide range of pH values (from6.5 to 7.5) is due to the fact that the solution absorbs carbon dioxideand oxygen in the air when stored in the air and gradually changesslightly in an acidic direction (the pH value is 6.5 to 7), or thesolution, when left in an atmosphere containing an alkaline gas, absorbsthe gas and changes to the direction of a weak alkalinity (the pH valueis 7 to 7.5).

According to the present invention, in contrast, the ceria particles aredispersed in water, and in addition the pH value is controlled. Asurface-active agent that does not contain Na may be added, ifnecessary, in addition to the acid and alkali. In order to keep theceria slurry alkaline, it is necessary for the hydrogen ionconcentration (i.e., the pH value) to be stable over 7.5. It isdesirable that the pH be over 8. A suitable material is an alkalinematerial, such as ammonia, water-holding hydrazine or amine containingneither Na nor K. In order to keep it acidic, on the other hand, the pHvalue may desirably be 6.5 or less by adding an acid of no or weakcorrosiveness. An acid containing no metal as its component, such asoxalic acid, sulfuric acid, phosphoric acid, succinic acid or citricacid, is suitable. Hydrochloric acid, nitric acid or hydrogen peroxidemay be added, if necessary. By using the aforementioned highly purecerium oxide particles A and B having well-controlled average particlediameters and by keeping the dispersion acidic or alkaline, ahigh-speed, stable, selective polishing characteristic is imparted.

By controlling the pH value of the ceria slurry using the cerium oxide Ato alkaline, the polishing rate of an organic insulating film could beincreased to a much higher value than those of the inorganic insulatingfilms regardless of whether they are doped or nondoped, as illustratedin FIG. 4(A). (Here, polishing a film selectively is defined asselective polishing). If, moreover, an acidic ceria slurry containingthis cerium oxide A is used, the polishing rates of doped insulatingfilms and nondoped insulating films can be substantially equalized tothose of organic insulating films. In the case of the ceria slurry usingthe ceria B, on the other hand, the polishing rates of inorganicinsulating films can be higher than those of the organic insulating filmin a range from weak acidity to alkalinity, as shown in FIG. 4(B).Moreover, the polishing rates of the doped insulating films can also behigher than those of nondoped insulating films.

By using the ceria slurry of the present invention, when an organicinsulating film is formed over a stepped wiring substrate having aninorganic insulating film formed on the surface and is polished by analkaline ceria slurry containing cerium oxide A of the presentinvention, the surface can be flattened quickly and easily while leavingthe organic insulating film in the recessed portion of the step withoutany substantial damage to the inorganic insulating film. The inorganicinsulating film can be used as a so-called "polishing stopper layer."

Since, moreover, the polishing rates of inorganic insulating films andorganic insulating films can be equalized, the roughness of the wiringsubstrate, on which they are present together, can be reduced bypolishing without deteriorating the flatness. When,on the contrary, adoped insulating film formed over a nondoped insulating film having arough surface is polished and this polishing must be ended when thenondoped insulating film is exposed, efficient operation can be achievedby using the ceria slurry containing the cerium oxide B having a pHvalue of 3 or more. The polishing effect is especially stable if the pHvalue lies on the alkaline side. By employing the ceria slurrycontaining the cerium oxide B, it is possible to use an organicinsulating film as the polish stopper layer of the inorganic insulatingfilm or to use a nondoped insulating film as the polish stopper layer ofthe doped insulating film. When, moreover, a two-layer insulating filmis used having a doped or nondoped insulating film formed over anorganic insulating film, it is preferable to use a ceria slurry whichcontains the cerium oxide B and which is not neutral, i.e., a ceriaslurry whose pH value is not less than 3 and not more than 14.

There exists no prior art rinsing method effective for removing ceriumoxide adhering after polishing. In the conventional manufacture ofoptical parts, there have been known only a physical wiping method usinga soft cloth or a brush and a method of liberating cerium oxideparticles by etching the surface to be polished with dilutedhydrofluoric acid. By the former method, the surface of the wiringsubstrate having the aforementioned fragile and non-dense film isdamaged. By the latter method, the insulating layer constituting thelayer to be polished contains SiO₂ as its main component and is liableto be damaged by a diluted hydrofluoric acid, so that the application ofthe method has been limited. However, it has been found that thescratches can be prevented by dipping the wiring substrate, after beingpolished with the ceria slurry,in the non-diluted, diluted, or mixedsolution of sulfuric acid, nitric acid, ammonium carbonate or ammonia.However, this process of removing the particles by those solutions isslow and the resulting concentration may not be low enough high. Ifnecessary, therefore, the liquid temperature is elevated to 50° C. orhigher, and hydrogen peroxide is added to the liquid, or the liquid isbubbled with ozone. The liquids thus treated are effective to react withthe ceria particles themselves to dissolve them, so that the particleremoving effect is less influenced by the material of the surface of thewiring substrate. Moreover, those treating liquids can be selectivelyused to avoid damaging the wiring substrate surface material. It isquite natural that the rinsing effect is enhanced by applying ultrasonicvibrations or by agitating the liquid while dipping the wiring substratein the liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) and 1(B) are views for explaining the process for planarizingthe surface of an element isolating buried layer of a wiring substrate;

FIGS. 2(A) and 2(B) are views for explaining the process for planarizingan organic insulating film on the surface of a wiring substrate;

FIGS. 3(A) and 3(B) are views for explaining the process for planarizingthe surface of a doped insulating film on the surface of a DRAM; and

FIGS. 4(a) and 4(b) are diagrams showing the relation between thepolishing rate of the ceria slurry, and the pH value.

DESCRIPTION OF EXAMPLES Example 1

Example 1 of the present invention will be described with reference toFIGS. 1(A) and 1(B). Over the surface of a wiring substrate 10 ofsilicon, as shown in FIG. 1(A), there was provided a two-layer filmwhich was composed of a first inorganic insulating film 11 of siliconoxide having a thickness of 10 nm and a silicon nitride film 12 having athickness of 10 nm and which was machined into a predetermined shape.The wiring substrate 10 was etched, at its portions uncovered with thetwo-layer film, to a depth of 0.5 μm. In these etched recesses,there wasformed a buried layer 13 of silicon oxide having a thickness of 0.7 μmby a CVD method. Next,the buried layer 13 was polished with an alkalineceria slurry (pH value is 10) using cerium oxide B, as shown in FIG.1(B). The polishing load adopted was 0.15 Kg/cm², and the buried layer13 was polished by the ceria slurry without changing the polishingcloths or the like if the polishing load was within a range of 0.1 to0.5 Kg/cm². This condition was adopted because the polishing rate dropsbut the planarity improves under such a low polishing load. Thepolishing platen and the slurry (although not shown) were kept at theroom temperature. The relative velocity between the wiring substrate 10and the polishing platen was about 30 m/min. Under these polishingconditions, the removal rate using a conventional silica slurry usingcolloidal silica was about 10 to 20 nm/min. at the highest, but theremoval rate using the ceria slurry was as high as 50 to 150 nm/min. Asthe polishing operation progressed, the silicon nitride film 12 wasexposed, and the polishing did not seem to progress. At this stage, thepolishing was ended. In these ways, elements such as transistors wereformed in those regions of the wiring substrate 10, which were isolatedby the buried layer 13. Incidentally, the alkaline ceria slurry of thecerium oxide B was used in the example but may be replaced by an acidceria slurry of the cerium oxide A. In the latter case, the removal ratemore or less drops, but the removal rate is advantageously stableirrespective of the film quality of the buried layer 13. A highlyselective polishing can be performed because the silicon nitride film 12is hardly polished by the ceria slurry. After this polishing step, thewiring substrate 10 was dipped in a mixture of sulfuric acid andhydrogen peroxide. The cerium oxide particles were quickly etched out,so that the surface of the wiring substrate 10 was sufficientlyplanarized and cleaned.

Example 2

Example 2 of the present invention will be described with reference toFIGS. 2(A) and 2(B). First, FIG. 2(A) shows a wiring substrate 20 inwhich on the interconnection 21 of an aluminum alloy (hereinaftershortly referred to as "Al") having a thickness of about 1 μm a firstinsulating film 22 made of SiO₂ having a thickness of 2 μm was formed bya PECVD (Plasma Enhanced Chemical Vapor Deposition) method. Next, anorganic insulating film 23 having a thickness of 1.2 μm was formedthereover by a coating method. This means that the coating was performedunder the condition that the thickness of 1.2 μm would be achieved for asubstrate having no roughness, but the thickness of the film applied ona rough surface of a substrate is naturally not even. The film thicknessis the one which was measured after the film was dried after the coatingand the solvent was almost completely removed, if not otherwisespecified. Here, the organic insulating film 22 was made of HSG R7 (thetrade name of a product by Hitachi Chemical Co., Ltd.). After thecoating, a heat treatment was carried out at the highest temperature of450° C. Next, the applied organic insulating film 23 was polished bypressing the wiring substrate 20, while being rotated, and by drippingthe (not-shown) ceria slurry which contained the cerium oxide A andwhose pH value was kept at 10, onto the (not-shown) polishing platen onwhich was stuck a sheet of a polyurethane resin, fluoroplastic, or thelike. The polishing condition was substantially identical to that ofExample 1. The removal rate of the organic coating insulating film 23 atthis time was about five times as high as that using a conventionalslurry containing colloidal silica under the identical condition.Incidentally, the first insulating film 22 of a PECVD SiO₂ film ishardly polished by the ceria slurry and therefore the margin for judgingthe end point of the polishing increases. Any material may be used forthe organic insulating layer 23 as long as it contains 5% or more oforganic component. The material for the inorganic insulating layer 22may be a doped or nondoped inorganic insulating substance.

After the polishing, the wiring substrate was dipped in a mixture ofnitric acid and hydrogen peroxide for 0.5 minutes or longer, in order toetch the cerium oxide so that the ceria slurry was removed from thewiring substrate 20, and the substrate 20 was effectively cleaned. Afterthis, the wiring substrate 20 was either neutralized by an ammonia-basedalkaline solution or cleaned to remove adhering matters other than theceria slurry with an organic solvent, if necessary. Next, a secondinorganic insulating film 24 of SiO₂ having a thickness of 0.4 μm wasformed by a PECVD method, if necessary.

Incidentally, the inorganic insulating film 22 does not have to beformed all over the Al interconnection but may be formed only on thefaces of the Al wiring lines 21. As the polishing of the organicinsulating film 23 progresses and the first insulating layer 22 isexposed, the polishing stops when the surface is flattened and theorganic insulating film 22 is buried.

Example 3

Example 3 of the present invention will be described with reference toFIGS. 3(A) and 3(B). FIG.3(A) shows a cross section of the device of anintegrated memory circuit (Dynamic Random Access Memory, hereinafterreferred to as the "DRAM") requiring "refreshing" in the stageimmediately before the metal electrodes of transistors are formed.Incidentally, the lefthand side shows the so-called "memory cellsection" for storing memory information, and the righthand sideschematically shows the transistor section of a peripheral circuit fordriving the memory cells. In order to enhance the integration of a DRAMhighly to 16 Mbits or more per chip, there has been generally used astructure called the "Stacked Capacitor Cell." As shown in FIG. 3(A),there are formed a gate 32 of the transistor, which is enclosed by afirst insulating film 31 for isolating the elements on the surface of awiring substrate 30 and a second insulating film 33 of SiO₂ formed by aCVD method, and first and second capacitor electrodes 34 and 35 forcapacitance accumulation through an insulating film (not shown). Theseare covered with a third insulating film 36 of a nondoped insulatingfilm having a thickness of 0.3 μm. Over this third insulating film 36,there is formed a fourth doped insulating film 37 containing 4%phosphorus and 10% boron and having a thickness of 1.5 μm. Due to thepresence of the aforementioned capacitor electrodes, the surface of thefourth insulating film 37 of the memory cell section (lefthand half ofFIG. 3(A)) is higher by 1.0 μm on an average than the peripheral circuitsection (of the righthand half). Such a large step may be a cause ofreduction of the processing accuracy at the lithography step and at thedry etching step. Then, the surface of the fourth insulating film 37 waspolished by an alkaline ceria slurry using the cerium oxide B. Thepolishing condition was substantially identical to that of the foregoingExamples. Since the polishing rate of the Sio₂ film containingphosphorus and boron is higher by two times or more than that of thenondoped insulating film, it was easy to stop the polishing when boththe third insulating film 36 below the fourth insulating film 37 of thememory cell portion and the bulging surface 36a were exposed. When usingcolloidal silica, however, the doped insulating film is polished at ahigh polishing rate, so that ratio of the removal rates of polishingusing colloidal silica and the ceria slurry of the present invention arealso about five.

After the polishing, the wiring substrate 30 was cleaned with 10%ammonium solution, and the substrate was subjected to the steps offorming via holes and forming metal electrodes of the transistors(neither of them is shown).

Since the height of the step between the memory cell section and theperipheral circuit section was decreased to 0.3 μm or less by thepolishing, the processing accuracies of the lithography and dry etchingwere kept at sufficiently high levels. Incidentally, the Figures of theExample show the substrate in which the surface of the fourth insulatingfilm 37 was smoothed by a heat treatment at a sufficiently hightemperature (a description has been already made that the smoothing stepis not essential for the present Example). This smoothing is realizedgenerally at first by forming a doped insulating film containingphosphorus and boron by a CVD method at a substrate temperature of 350to 400° C. and subsequently by performing a heat treatment at 850 to900° C. to stabilize the phosphorus and to fluidize the film surface. Inorder to prevent the characteristics of the very fine transistorelements or the (not-shown) capacitor insulating film from beingdeteriorated, however, it is desired to lower the heat treatmenttemperature below 800° C. At a temperature below 850° C., phosphorus andboron in the doped insulating film 37 can be stabilized but smoothingthe surface of the film 37 is difficult. Therefore one may believe thatthe technique requiring fluidization has come to its limit. However,phosphorus can be stabilized according to the present invention bysubjecting the doped insulating film 37 to a heat treatment of 450° C.or higher. Without the surface smoothing step by the fluidization,therefore, according to the present invention planarizing with aresidual step of 0.3 μm or less is realized by polishing.

After polishing, the wiring substrate 30 is dipped in a liquidcontaining an aqueous solution of 10% ammonium carbonate and a hydrogenperoxide solution at a ratio of 1:1. As a result, the ceria slurry isdissolved or removed from the wiring substrate 30, and the substrate iscleaned.

According to the present invention, a fragile inorganic or organicinsulating film, which was prepared at a relatively low temperature, canbe polished without causing any deterioration of the currentcharacteristics of the semiconductor elements due to Na diffusion or thelike.

What is claimed is:
 1. A method for treating a polishing agent,whereincerium oxide is removed from a wiring substrate polished by said ceriumoxide, by using a solution including at least one of sulfuric acid andnitric acid, bubbled with a gas containing ozone.
 2. A method fortreating a polishing agent,wherein cerium oxide is removed from a wiringsubstrate polished by said cerium oxide, by using solution including atleast one of ammonium carbonate and ammonia, bubbled with a gascontaining ozone.